Black hole superradiance is a powerful probe of ultralight axions. If nature contains a boson with a mass of order ${10}^{-12}\mathrm{eV}$, mere vacuum fluctuations will lead to its efficient production around spinning stellar mass black holes, forming a gravitational atom that both drains the black hole spin and decays to produce near-monochromatic gravitational waves. Existing superradiance constraints derive primarily from spin measurements of a handful of identified black holes. Here we instead present a detailed study of the population level effect: gravitational waves arising from both the 100 million black holes in the Milky Way and the stochastic signal from axion clouds throughout the universe. We study the impact of a broad range of systematic uncertainties on the black hole properties and compute the projected axion sensitivity for LIGO, as well as the future instruments Einstein Telescope, Cosmic Explorer, and a high-frequency magnetic Weber bar. We demonstrate that LIGO can robustly probe axion masses from roughly ${10}^{-13}\mathrm{eV}$ to $4\times {10}^{-12}\mathrm{eV}$. If the black hole population extends to masses slightly below $5M_{\odot }$—as hinted for by LIGO inspiral observations—LIGO would approach ${10}^{-11}\mathrm{eV}$. Under that same assumption we show that a future high-frequency detector could push considerably higher, potentially beyond ${10}^{-10}\mathrm{eV}$ in the most optimistic scenarios, reaching toward the lowest masses within the projected sensitivity of axion dark matter searches.

We present results on the Mellin moments of the unpolarized parton distribution function (PDF) of the pion and kaon up to the fourth order. The computation is done using one $N_f=2+1+1$ gauge ensemble of twisted mass fermions with quark masses tuned to approximately their physical values. We reconstruct the valence pion and kaon PDFs using the connected contributions to the three Mellin moments. We compare our results on the Mellin moments and the reconstructed PDFs with other lattice QCD and phenomenological determinations.

In the present work, we investigate the long-distance contributions to light hadrons and radiative decays of ${\eta }_c$, where the long-distance contribution is phenomenologically described by the meson loops. Our estimations indicate that the branching fractions of ${\eta }_c\to \mathcal{V}\mathcal{V},\mathcal{V}=(\rho ,\omega ,\varphi )$, can be roughly reproduced in the range $1.4<\alpha <1.6$, while the parameter range for ${\eta }_c\to \gamma \mathcal{V}$ is determined by the similarity of ${\eta }_c\to \gamma \mathcal{V}/\mathcal{V}\mathcal{V}$ and ${\chi }_{c1}\to \gamma \mathcal{V}/\mathcal{V}\mathcal{V}$. In this parameter range, our estimations indicate that the branching fractions for the processes ${\eta }_c\to \gamma {\rho }^0$ and ${\eta }_c\to \gamma \omega$ are of the order of ${10}^{-4}$, while the one for the process ${\eta }_c\to \gamma \varphi$ is of the order of ${10}^{-5}$. The estimations in the present work are expected to be accessible by future experiments at BESIII and Belle II.

In this work, we have investigated the physical properties like decay constants, radiative transitions, decay widths, and branching ratios for the ground and radially excited charmonia states. For the numerical calculations, we have adopted the light-front quark model. We have studied ${\chi }_{c0}\to J/\psi +\gamma$ and $\psi (2S)\to {\chi }_{c0}+\gamma$, $h_c(1P)\to {\eta }_c(1S)+\gamma$, and ${\eta }_c(2S)\to h_c(1P)+\gamma$ transitions in this work. We have also studied the $Q^2$ dependence of the electric dipole transition form factors (TFFs) for all four transitions and compared them with the available lattice QCD and basis light-front quantization results. Using the TFF results, we have calculated the decay widths and branching ratios for these transitions. The electric dipole matrix element is decomposed into its Lorentz structures and $E_1(Q^2)$ is extracted from a combination of the longitudinal and transverse plus-current amplitudes canceling the accompanying Coulomb form factor identically. The light-front spin-orbit wave functions of the $P$-wave states ${\chi }_{c0}$ (${}^3{P}_0$) and $h_c$ (${}^1{P}_1$) are constructed from the Melosh transformation of the corresponding $|(LS)J{J}_z⟩$ states, rather than from the $S$-wave pseudoscalar and vector ones. The charm quark mass and the harmonic scale are fixed by a variational fit to the two $1S$ masses alone. Our numerical results of decay constants, decay widths, and branching ratios are overall in good agreement with available experimental, theoretical, and lattice simulation data.

We perform a diffusion Monte Carlo study of fully light hexaquarks containing three $u$ quarks and three $d$ quarks within a constituent-quark model. Both compact and baryon-baryon-like arrangements were considered separately. All compact hexaquark configurations are found well above their corresponding baryon-baryon thresholds, suggesting that deeply bound compact six-quark states are not favored in the light-quark sector within this model. By contrast, several dibaryonlike configurations lie close to, but above, the $NN$, $N\mathrm{\Delta }$, and $\mathrm{\Delta }\mathrm{\Delta }$ thresholds and show spatial structures compatible with molecular states. One configuration exhibits two well-defined nucleonlike subclusters separated by several femtometers, characteristic of deuteronlike spatial clustering, although its calculated energy remains slightly above the corresponding threshold.

We point out that the masses of the highly excited bound quark-antiquark states in ${\mathrm{QCD}}_2$ in the infinite $N$ limit may be determined in the framework of a simple quantum-mechanical model with the potential $V(x)=\sigma |x|$. In the ultrarelativistic case, the masses follow the pattern ${\mu }_n^2=\frac{\pi g^{2}N}{2}n$, which coincides with the law derived by ‘t Hooft by solving the Bethe-Salpeter equation. In the nonrelativistic case, the levels follow the asymptotics ${\epsilon }_n={\mu }_n-2m=C{n}^{2/3}$, where the constant $C$ can be determined by solving the ‘t Hooft equation or, alternatively, the nonrelativistic Schrödinger equation.

The quest to understand the properties of matter at supranuclear densities found in the cores of neutron stars has intrigued physicists for a long time. The study addresses this problem using a physics-informed machine learning approach guided by astrophysical observations. The transformer model is trained on an agnostically generated ensemble of equations of state. Two geometric parameters are defined on the mass-radius sequence of a neutron star—the front bending and the back bending. The model provides a two-step solution: first, the model predicts the maximum mass and radius using the bending parameters, and then reconstructs the square of the sound-speed profile, completing the inverse mapping to the equation of state. Our results show that massive neutron stars are associated with sound-speed profiles that peak at relatively low densities, leading to strong back bending and a low-density stiff equation of state, indicating an early transition to quark matter and making the density at the core of massive stars comparatively less. The maximum mass for a neutron star predicted by the astrophysical constrained transformer model is 2.477 solar masses, and a minimum radius of about 11.498 km for a canonical mass of 1.4 solar masses.

It has long been believed that newborn quark stars are inefficient emitters because the quark plasma frequency is so high that it suppresses electromagnetic radiation across the entire spectrum up to energies of several tens of MeV. Here, we show that significant electromagnetic emission can instead originate from the electrosphere of a quark star, where the plasma frequency is much lower, approximately 40 keV. As a result, the cooling of a newborn quark star is expected to proceed through two distinct observational epochs. During the first epoch, blackbody radiation is emitted from the photosphere of an optically thick relativistic wind generated near the electrosphere. For 2SC+ quark star, over the course of a few days following its formation, the photospheric temperature decreases from several MeV to about 22 keV. During the second epoch, the blackbody spectrum evolves into a narrow feature centered around 40 keV, and the emission gradually fades. This spectral evolution provides a characteristic signature of the electrosphere surrounding compact astrophysical objects and may be detectable with current or future x-ray observatories.

We extend the investigation into the formation of shell-crossing singularities (SCSs) in effective polymerized Lemaître-Tolman-Bondi (LTB) models to the loop-quantum-gravity-inspired asymmetric bounce model, as well as to effective LTB models based on the solutions of Bardeen and Hayward, in which no bounce occurs. While the asymmetric bouncing model belongs to the class of bounded polymerization functions, the latter models feature unbounded polymerization functions. Our results show that, similar to the symmetric bouncing model, for the asymmetric bouncing model SCSs are unavoidable for inhomogeneous dust profiles. In contrast, for models without a bounce and with unbounded polymerization functions, no SCSs form for inhomogeneous, decreasing dust profiles—a situation that resembles classical theory, in which SCSs can also be avoided by a suitable choice of initial data.

We investigate Nielsen’s geometric approach to quantum complexity in the presence of multiple cost factors, extending the standard framework where a single penalty distinguishes easy from hard directions of the group manifold. By introducing a hierarchy of penalties associated with different degrees of nonlocality, we develop a generalized right-invariant complexity geometry and analyze its implications for geodesic evolution. We derive the modified Euler-Arnold and Jacobi equations and study how multiple cost factors reshape the structure and scaling of conjugate points, where geodesic optimality breaks down. The formalism is illustrated in two settings: a single-qubit system with two cost factors, where we develop a semianalytic approach to investigate complexity growth and its dependence on penalty hierarchies, and Sachdev-Ye-Kitaev-type models, where we analyze both free and chaotic regimes. In these many-body systems, we show that distinct nonlocal sectors generate multiple families of conjugate points whose occurrence depends on both the cost hierarchy and the system size. Our results highlight how refining the penalty structure provides a richer and more realistic description of quantum complexity and its dynamical behavior.

Quantum anomalies give rise to novel transport phenomena, including the generation of a current in a relativistic fluid due to the presence of magnetic field or vorticity. We present an exclusive and direct computation of the chiral anomaly in the adiabatic regime within the path integral for a massless fermion on a generic electromagnetic and curved background, including local temperature and chemical potential. We identify new quantum-thermodynamical contributions to the breaking of axial symmetry which induce the chiral separation and vortical effects.

We provide a thorough study of the properties of the Boulware vacuum in the spacetime of a spherical, static thin shell with a Minkowski interior. To this end, we calculate the renormalized vacuum polarization and stress-energy tensor of massless scalar fields via the extended-coordinate prescription, paying particular attention to their scaling as the shell approaches the black hole limit. Near the surface of the thin shell, we obtain the expected leading-order singular behavior of both quantities via two independent methods: a high-frequency approximation for the modes and a weak-field approximation. At the center of the shell we find nonlocal, Casimir-like contributions that remain finite in the black hole limit, and whose backreaction effects we compute via the semiclassical Einstein equations. Away from these regions amenable to analytic treatment, we obtain numerical results for a wide range of shell compactnesses and field couplings. In the black hole limit, we show that the vacuum polarization and renormalized stress-energy tensor outside the shell quickly approach the ones generated by a Schwarzschild black hole, suggesting a possible universality in the vacuum outside highly compact horizonless objects. This work addresses the conceptual and technical aspects necessary for computing renormalized expectation values in matter configurations, laying the foundations for future explorations on the subject.

Spectra of standard one-dimensional potentials (double-well, sin-Gordon, etc.) are given by trans-series in coupling, including (badly divergent) perturbative series and nonperturbative terms $\sim \exp (-\mathrm{const}/g^2)$ and $\log (1/g)\exp (-\mathrm{const}/g^2)$. All of them are badly defined (e.g., perturbative series are badly divergent) but in sum supposed to be good. In this paper, we discuss an example of a potential with specially defined couplings making perturbative series completely absent. We calculate its nonperturbative vacuum energy and show that they are reproduced by the action of certain complex solutions to the holomorphic Newton equation.

To model a compact binary coalescence, it is commonly assumed that the binary evolves in isolation. In the present work, we relax this assumption by introducing a distant third body and investigating how the third body would affect the binary evolution. We treat this problem perturbatively and study tidal interaction in the binary due to the third body’s presence. We introduce appropriate modifications to the equations governing the orbital motions and the evolution equations of the binary component’s quadrupole moment. We compute the radiated energy and accumulated dephasing for the binary. Our findings indicate that for extreme-mass-ratio inspirals, these effects would not be significant. However, for binaries such as intermediate-mass-ratio inspirals, these effects are more relevant, and in some scenarios, the accumulated dephasing can reach up to $\mathcal{O}(1)$ radians.

We present an exact solution to the Einstein-Maxwell equations that describes a static black hole coexisting with anisotropic matter immersed in an external magnetic field, obtained via the Harrison transformation. Our findings reveal that an increase in the anisotropic matter parameter systematically suppresses the local chaotic behavior, as indicated by a reduction in the Lyapunov exponent. Conversely, variations in the external magnetic field lead to qualitative changes in global chaotic behavior. This is analyzed through Poincaré sections, which demonstrate transitions between regular and chaotic trajectories resulting from the nonlinear gravitational-magnetic interactions. These factors play distinct yet complementary roles in shaping chaotic particle dynamics around black holes. This study would offer a new theoretical framework for exploring nonintegrable particle motion within magnetized black hole spacetimes.

We study electromagnetic perturbations and the associated quasinormal modes (QNMs) of parametrized static, spherically symmetric wormhole spacetimes, focusing on Damour-Solodukhin and braneworld geometries as well as their galactic extensions. Using the Bronnikov-Konoplya-Pappas (BKP) parametrization, we express the metric functions in terms of a compactified radial coordinate and characterize the spacetime through far-field and near-throat parameters. The far-field coefficients govern the asymptotic structure and post-Newtonian behavior, while the near-throat continued-fraction expansion captures the strong-field geometry near the throat. We first apply the parametrization to isolated wormholes and identify its range of validity, showing that the nonanalytic metric functions can limit the applicability of the BKP scheme. Moreover we have shown that such issues can indeed hamper the primary ringdown waveform. We then extend the framework to a galactic Damour-Solodukhin wormhole embedded in a Hernquist dark matter halo. Imposing observational bounds from the shadow of Sgr ${\mathrm{A}}^{*}$, we constrain the galactic compactness and deformation parameters and obtain an observationally viable parametrized metric. Within the allowed parameter space, we compute the fundamental QNM frequencies using the transfer matrix method and analyze the corresponding time-domain ringdown signals. We find that the damping rate is more sensitive to galactic compactness, whereas the oscillation frequency remains comparatively stable. Although the spectral shifts are small within the shadow-allowed region, the framework provides a systematic link between geometric parametrization, shadow constraints, and dynamical response. Our results establish an observationally consistent parametrized description of wormhole perturbations for strong-field tests of horizonless compact objects.

It has recently been revealed [Gervalle and Volkov, Phys. Rev. Lett. 133, 171402 (2024)] that spatially regular bound-state matter configurations which are made of electroweak fields can be supported by magnetically charged black holes of the Einstein-Weinberg-Salam field theory. Intriguingly, it has been demonstrated numerically that the dimensionless mass parameter $\mu \equiv m_{\mathrm{w}}{r}_{+}$ of cloudy black-hole-field configurations, magnetically charged Reissner-Nordström black holes that support linearized electroweak fields, is characterized by a discrete resonant spectrum $\{{\mu }_k(n){\}}_{k=0}^{k=\infty }$ (here $\{r_{+},n\}$ are respectively the horizon radius and the discrete magnetic parameter of the central black hole and $m_{\mathrm{w}}$ is the mass of the supported W-boson field). In the present paper we explore the excited resonant spectrum of the Einstein-Weinberg-Salam field theory. In particular, using analytical techniques we derive a remarkably compact formula for the low-mass (${\mu }_k\ll 1$) resonant spectrum of composed weakly magnetized-black-hole-linearized-electroweak-field bound-state configurations. Interestingly, it is shown that the excited black-hole-field resonances are characterized by the simple universal ($\{m_{\mathrm{w}},r_{+}\}$-independent) relation ${\mu }_{k+1}/{\mu }_k=e^{-2\pi /\sqrt{2n-1}}$. Finally, it is explicitly shown that our analytically derived formula for the discrete resonance spectrum of the composed black-hole-field system agrees remarkably well with the corresponding numerical data that recently appeared in the physics literature.

We consider the possibility that the stochastic gravitational wave (GW) background suggested by pulsar timing array (PTA) datasets is sourced by primordial black holes (PBHs). Specifically, we perform a Bayesian search in the International PTA data release 2 (IPTA DR2) for a combined GW background arising from scalar perturbations and unresolved PBH mergers, assuming a broad PBH mass distribution. In our analysis, we incorporate constraints on the curvature power spectrum from cosmic microwave background $\mu$ distortions and the overproduction of PBHs, which significantly suppress the contribution of PBH mergers to the total GW background. We find that scalar-induced GWs dominate the nanohertz frequency range, while PBH mergers alone cannot account for the observed signal under the standard PBH formation scenario involving Gaussian perturbations and including only Poissonian PBH clustering. However, specific PBH models, such as those with enhanced clustering, could yield a GW background dominated by PBH mergers. Overall, we find that the IPTA DR2 strongly favors an astrophysical origin for the reported common-spectrum process over the PBH models considered in this analysis.

The data on cosmic antiprotons have reached an outstanding precision on energies spanning from GeV to hundreds of TeV, thanks to the space-based AMS-02 experiment. The balloon-borne GAPS experiment, which just completed its first Antarctic flight, will address antiproton and antideuteron fluxes well below GeV energies. Antinuclei in cosmic rays, as well as being produced by spallation reactions between cosmic-ray nuclei and the atoms of the interstellar medium, may hide contributions from exotic sources, such as particle dark matter annihilation in the Galaxy. In this paper, we present predictions for cosmic antiproton, antideuteron and antihelium fluxes both from secondary and dark matter origin. We use state-of-the-art production spectra, nuclear coalescence for antinuclei, and Galactic propagation models to derive upper limits on the dark matter annihilation cross section from AMS-02 antiproton data in different propagation scenarios (BIG and QUAINT). We quantify the impact of future GAPS data, showing that its sensitivity to sub-GV antiprotons could improve the $⟨\sigma v⟩$ constraints by up to an order of magnitude for light DM ($m_{\chi }\lesssim 50\mathrm{GeV}$). For heavier antinuclei, the detection perspective with existing and upcoming experiments are derived for those scenarios consistent with AMS-02 antiproton flux. The detectability of such signals strongly depends on the experiment, the propagation model, and the hadronization tuning. Our analysis underscores the complementarity of antinuclei channels for indirect DM searches and the critical role of low-energy windows in constraining light DM candidates.

We investigate the projected sensitivity of the Future Circular Collider in $e^{+}{e}^{-}$ mode (FCC-ee) in probing the lepton flavor violating (LFV) decay of the 125 GeV Higgs boson, $h\to \mu \tau$, $h\to e\tau$, and $h\to e\mu$ at center-of-mass energy of 240 GeV with an integrated luminosity of $5{\mathrm{ab}}^{-1}$. With the clean multilepton final states, we consider the Higgs production modes that contribute to $e^{+}{e}^{-}\to \ell \ell h$, in particular, the Higgs-strahlung and the vector boson fusion production channels. The 95% confidence level upper limits on branching ratio are found to be $5.94\times {10}^{-4}$, $6.28\times {10}^{-4}$, and $7.37\times {10}^{-5}$ for the channels $h\to \mu \tau$, $h\to e\tau$, and $h\to e\mu$, respectively. In addition, we also consider the LFV decay of a new $\mathrm{CP}$-even Higgs boson with mass in the range of 110–200 GeV. The projected FCC-ee sensitivities are then compared to those from low-energy searches for $\ell \to {\ell }^{\prime }\gamma$ decay. We find that the FCC-ee sensitivity for the LFV decays of the Higgs boson in the $e-\tau$ and $\mu -\tau$ channels is superior to the low-energy constraints. However, in the $e-\mu$ case, the low-energy search offers stronger constraints.